Polyvinyl alcohol is the largest volume, synthetic, water-soluble and biodegradable resin produced in the world. Its success is due in part to its excellent chemical resistance and physical properties as well as to its very low toxicity. The main applications for polyvinyl alcohol are in textile sizing, adhesives, polymerization stabilizers and paper coatings. As demand increases for better performance in these and other areas, more attention is given to production of polyvinyl alcohol derivatives which can meet the demand. Chemically modifying polyvinyl alcohol by introducing functional groups (for example, sulfonates, phosphates and carboxylates) through copolymerization or post-modification is one means of enhancing the physical properties of polyvinyl alcohol.
Copolymerization of vinyl acetate with functional vinyl monomers followed by saponification is a well-known route to modification of polyvinyl alcohol. Some applications of this technology are exemplified in the following patents:
JP 56-73199 teaches copolymerization of vinyl acetate with 2-acryl amidopropanesulfonic acid or its metal salts, to produce a polymer with improved flow properties for application in paper coatings.
U.S. Pat. No. 4,529,522 teaches production of copolymers of polyvinyl alcohol and ethylene oxide or propylene oxide sulfonate ethers for use as viscosifiers in saline solutions.
JP 60-56196 teaches copolymerization of vinyl acetate with 0.1 to 0.3 mole percent sodium vinyl sulfonate or sodium allyl sulfonate and hydrolysis of 30 to 60 percent the resulting copolymer. The product is used in hot melt adhesives.
JP 63-270704 teaches the manufacture of high polymerization degree sulfonic acid-containing modified polyvinyl alcohol by copolymerizing N-sulfoalkyl(meth)acrylamide and vinyl ester and then saponifying the resulting copolymer. The products are useful as emulsifiers.
Copolymerization allows the incorporation of a wide variety of functional monomers, but entails large capital investment for recovery of unreacted monomer. Differences in reactivity ratios may also make it difficult to produce the desired functional level and tool molecular weight.
Production of specialized grades of modified polyvinyl alcohol in small to moderate volumes can be more economically achieved through post-modification. Post-modification also provides a versatile process for producing a variety of specialized products using a single process unit.
Post-modification of polyvinyl alcohol is usually carried out in water solution. See Polyvinyl Alcohol, edited by C. A. Finch, Wiley, 1973, pages 183-202, for an exhaustive list of reactions for polyvinyl alcohol in solution. Following are examples of solution modification in the patent literature are:
EP-128,345 teaches the reaction of polyvinyl alcohol with alkenal-3-sulfonic acid in aqueous solution to form a product used in textile sizing or emulsifiers.
U.S. Pat. No. 4,545,911 teaches grafting pyrrolidium methane sulfonate salt onto the alcohol oxygens of polyvinyl alcohols to form viscosifiers which are useful in waterflooding and in drawing fluids.
A few post-modification processes are known for slurry or solid state reactions.
U.S. Pat. No. 3,125,556 teaches the alkoxylation of polyvinyl alcohol in which an organic polar swelling agent may be added to the polyvinyl alcohol prior to alkoxylation.
U.S. Pat. No. 4,775,715 teaches preparation of cationic polyvinyl alcohol by blending polyvinyl alcohol under high shear conditions, at 0.degree. to 100.degree. C. with a small amount of water, a small excess of base, and a quaternizing agent.
JP 1-34245 teaches a method for preparing a polyvinyl alcohol type resin containing an acetoacetic ester by mixing a finely divided polyvinyl alcohol powder with diketene in a high intensity mixer.
U.S. Pat. No. 4,822,851 and U.S. Pat. No. 5,001,191 teach a dry blending process for the preparation of cationized polyvinyl alcohol in which polyvinyl alcohol, preferably in powder form, reacts with alkylidene epoxides in an alkaline medium in the presence of water.